/*
 * MinIO Cloud Storage, (C) 2020 MinIO, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package cmd

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"runtime/debug"
	"strings"
	"sync"
	"time"

	"github.com/klauspost/compress/s2"
	"github.com/minio/minio/cmd/logger"
	"github.com/minio/minio/pkg/hash"
	"github.com/tinylib/msgp/msgp"
)

//go:generate msgp -file $GOFILE -unexported

// a bucketMetacache keeps track of all caches generated
// for a bucket.
type bucketMetacache struct {
	// Name of bucket
	bucket string

	// caches indexed by id.
	caches map[string]metacache

	// Internal state
	mu        sync.RWMutex `msg:"-"`
	updated   bool         `msg:"-"`
	transient bool         `msg:"-"` // bucket used for non-persisted caches.
}

// newBucketMetacache creates a new bucketMetacache.
// Optionally remove all existing caches.
func newBucketMetacache(bucket string, cleanup bool) *bucketMetacache {
	if cleanup {
		// Recursively delete all caches.
		objAPI := newObjectLayerFn()
		ez, ok := objAPI.(*erasureServerSets)
		if ok {
			ctx := context.Background()
			ez.deleteAll(ctx, minioMetaBucket, metacachePrefixForID(bucket, slashSeparator))
		}
	}
	return &bucketMetacache{
		bucket: bucket,
		caches: make(map[string]metacache, 10),
	}
}

// loadBucketMetaCache will load the cache from the object layer.
// If the cache cannot be found a new one is created.
func loadBucketMetaCache(ctx context.Context, bucket string) (*bucketMetacache, error) {
	objAPI := newObjectLayerFn()
	for objAPI == nil {
		select {
		case <-ctx.Done():
			return nil, ctx.Err()
		case <-time.After(250 * time.Millisecond):
		}
		objAPI = newObjectLayerFn()
		if objAPI == nil {
			logger.LogIf(ctx, fmt.Errorf("loadBucketMetaCache: object layer not ready. bucket: %q", bucket))
		}
	}
	var meta bucketMetacache
	var decErr error
	var wg sync.WaitGroup
	wg.Add(1)

	r, w := io.Pipe()
	go func() {
		defer wg.Done()
		dec := s2DecPool.Get().(*s2.Reader)
		dec.Reset(r)
		decErr = meta.DecodeMsg(msgp.NewReader(dec))
		dec.Reset(nil)
		s2DecPool.Put(dec)
		r.CloseWithError(decErr)
	}()
	// Use global context for this.
	err := objAPI.GetObject(GlobalContext, minioMetaBucket, pathJoin("buckets", bucket, ".metacache", "index.s2"), 0, -1, w, "", ObjectOptions{})
	logger.LogIf(ctx, w.CloseWithError(err))
	if err != nil {
		if isErrObjectNotFound(err) {
			err = nil
		} else {
			logger.LogIf(ctx, err)
		}
		if errors.Is(err, InsufficientReadQuorum{}) {
			// Cache is likely lost. Clean up and return new.
			return newBucketMetacache(bucket, true), nil
		}
		return newBucketMetacache(bucket, false), err
	}
	wg.Wait()
	if decErr != nil {
		if errors.Is(err, context.Canceled) {
			return newBucketMetacache(bucket, false), err
		}
		// Log the error, but assume the data is lost and return a fresh bucket.
		// Otherwise a broken cache will never recover.
		logger.LogIf(ctx, decErr)
		return newBucketMetacache(bucket, true), nil
	}
	// Sanity check...
	if meta.bucket != bucket {
		logger.Info("loadBucketMetaCache: loaded cache name mismatch, want %s, got %s. Discarding.", bucket, meta.bucket)
		return newBucketMetacache(bucket, true), nil
	}
	return &meta, nil
}

// save the bucket cache to the object storage.
func (b *bucketMetacache) save(ctx context.Context) error {
	if b.transient {
		return nil
	}
	objAPI := newObjectLayerFn()
	if objAPI == nil {
		return errServerNotInitialized
	}

	// Keep lock while we marshal.
	// We need a write lock since we update 'updated'
	b.mu.Lock()
	if !b.updated {
		b.mu.Unlock()
		return nil
	}
	// Save as s2 compressed msgpack
	tmp := bytes.NewBuffer(make([]byte, 0, b.Msgsize()))
	enc := s2.NewWriter(tmp)
	err := msgp.Encode(enc, b)
	if err != nil {
		b.mu.Unlock()
		return err
	}
	err = enc.Close()
	if err != nil {
		b.mu.Unlock()
		return err
	}
	b.updated = false
	b.mu.Unlock()

	hr, err := hash.NewReader(tmp, int64(tmp.Len()), "", "", int64(tmp.Len()), false)
	if err != nil {
		return err
	}
	_, err = objAPI.PutObject(ctx, minioMetaBucket, pathJoin("buckets", b.bucket, ".metacache", "index.s2"), NewPutObjReader(hr, nil, nil), ObjectOptions{})
	logger.LogIf(ctx, err)
	return err
}

// findCache will attempt to find a matching cache for the provided options.
// If a cache with the same ID exists already it will be returned.
// If none can be found a new is created with the provided ID.
func (b *bucketMetacache) findCache(o listPathOptions) metacache {
	if b == nil {
		logger.Info("bucketMetacache.findCache: nil cache for bucket %s", o.Bucket)
		return metacache{}
	}

	if o.Bucket != b.bucket && !b.transient {
		logger.Info("bucketMetacache.findCache: bucket %s does not match this bucket %s", o.Bucket, b.bucket)
		debug.PrintStack()
		return metacache{}
	}

	debugPrint := func(msg string, data ...interface{}) {}
	if false {
		debugPrint = logger.Info
	}

	// Grab a write lock, since we create one if we cannot find one.
	if o.Create {
		b.mu.Lock()
		defer b.mu.Unlock()
	} else {
		b.mu.RLock()
		defer b.mu.RUnlock()
	}

	// Check if exists already.
	if c, ok := b.caches[o.ID]; ok {
		debugPrint("returning existing %v", o.ID)
		return c
	}

	var best metacache
	for _, cached := range b.caches {
		// Never return transient caches if there is no id.
		if b.transient {
			break
		}
		if cached.status == scanStateError || cached.dataVersion != metacacheStreamVersion {
			debugPrint("cache %s state or stream version mismatch", cached.id)
			continue
		}
		if cached.startedCycle < o.OldestCycle {
			debugPrint("cache %s cycle too old", cached.id)
			continue
		}
		// Root of what we are looking for must at least have
		if !strings.HasPrefix(o.BaseDir, cached.root) {
			debugPrint("cache %s prefix mismatch, cached:%v, want:%v", cached.id, cached.root, o.BaseDir)
			continue
		}
		// If the existing listing wasn't recursive root must match.
		if !cached.recursive && o.BaseDir != cached.root {
			debugPrint("cache %s  non rec prefix mismatch, cached:%v, want:%v", cached.id, cached.root, o.BaseDir)
			continue
		}
		if o.Recursive && !cached.recursive {
			debugPrint("cache %s not recursive", cached.id)
			// If this is recursive the cached listing must be as well.
			continue
		}
		if o.Separator != slashSeparator && !cached.recursive {
			debugPrint("cache %s not slashsep and not recursive", cached.id)
			// Non slash separator requires recursive.
			continue
		}
		if cached.ended.IsZero() && time.Since(cached.lastUpdate) > metacacheMaxRunningAge {
			debugPrint("cache %s not running, time: %v", cached.id, time.Since(cached.lastUpdate))
			// Abandoned
			continue
		}
		if !cached.ended.IsZero() && cached.endedCycle <= o.OldestCycle {
			debugPrint("cache %s ended and cycle (%v) <= oldest allowed (%v)", cached.id, cached.endedCycle, o.OldestCycle)
			// If scan has ended the oldest requested must be less.
			continue
		}
		if cached.started.Before(best.started) {
			debugPrint("cache %s disregarded - we have a better", cached.id)
			// If we already have a newer, keep that.
			continue
		}
		best = cached
	}
	if !best.started.IsZero() {
		if o.Create {
			best.lastHandout = UTCNow()
			b.caches[best.id] = best
			b.updated = true
		}
		debugPrint("returning cached %s, status: %v, ended: %v", best.id, best.status, best.ended)
		return best
	}
	if !o.Create {
		return metacache{
			id:     o.ID,
			bucket: o.Bucket,
			status: scanStateNone,
		}
	}

	// Create new and add.
	best = o.newMetacache()
	b.caches[o.ID] = best
	b.updated = true
	debugPrint("returning new cache %s, bucket: %v", best.id, best.bucket)
	return best
}

// cleanup removes redundant and outdated entries.
func (b *bucketMetacache) cleanup() {
	// Entries to remove.
	remove := make(map[string]struct{})
	currentCycle := intDataUpdateTracker.current()

	debugPrint := func(msg string, data ...interface{}) {}
	if false {
		debugPrint = logger.Info
	}

	b.mu.RLock()
	for id, cache := range b.caches {
		if b.transient && time.Since(cache.started) > time.Hour {
			// Keep transient caches only for 1 hour.
			remove[id] = struct{}{}
		}
		if !cache.worthKeeping(currentCycle) {
			debugPrint("cache %s not worth keeping", id)
			remove[id] = struct{}{}
		}
		if cache.id != id {
			logger.Info("cache ID mismatch %s != %s", id, cache.id)
			remove[id] = struct{}{}
		}
		if cache.bucket != b.bucket && !b.transient {
			logger.Info("cache bucket mismatch %s != %s", b.bucket, cache.bucket)
			remove[id] = struct{}{}
		}
	}

	// Check all non-deleted against eachother.
	// O(n*n), but should still be rather quick.
	for id, cache := range b.caches {
		if _, ok := remove[id]; ok {
			continue
		}
		for _, cache2 := range b.caches {
			if cache.canBeReplacedBy(&cache2) {
				debugPrint("cache %s can be replaced by %s", id, cache2.id)
				remove[id] = struct{}{}
				break
			} else {
				debugPrint("cache %s can be NOT replaced by %s", id, cache2.id)
			}
		}
	}

	b.mu.RUnlock()
	for id := range remove {
		b.deleteCache(id)
	}
}

// updateCache will update a cache by id.
// If the cache cannot be found nil is returned.
// The bucket cache will be locked until the done .
func (b *bucketMetacache) updateCache(id string) (cache *metacache, done func()) {
	b.mu.Lock()
	c, ok := b.caches[id]
	if !ok {
		b.mu.Unlock()
		return nil, func() {}
	}
	return &c, func() {
		c.lastUpdate = UTCNow()
		b.caches[id] = c
		b.mu.Unlock()
	}
}

// updateCacheEntry will update a cache.
// Returns the updated status.
func (b *bucketMetacache) updateCacheEntry(update metacache) (metacache, error) {
	b.mu.Lock()
	defer b.mu.Unlock()
	existing, ok := b.caches[update.id]
	if !ok {
		logger.Info("updateCacheEntry: bucket %s list id %v not found", b.bucket, update.id)
		return update, errFileNotFound
	}

	existing.lastUpdate = UTCNow()

	if existing.status == scanStateStarted && update.status == scanStateSuccess {
		existing.ended = UTCNow()
		existing.endedCycle = update.endedCycle
	}

	if existing.status == scanStateStarted && update.status != scanStateStarted {
		existing.status = update.status
	}

	if existing.error == "" && update.error != "" {
		existing.error = update.error
		existing.status = scanStateError
		existing.ended = UTCNow()
	}
	existing.fileNotFound = existing.fileNotFound || update.fileNotFound
	b.caches[update.id] = existing
	b.updated = true
	return existing, nil
}

// getCache will return a clone of a specific metacache.
// Will return nil if the cache doesn't exist.
func (b *bucketMetacache) getCache(id string) *metacache {
	b.mu.RLock()
	c, ok := b.caches[id]
	b.mu.RUnlock()
	if !ok {
		return nil
	}
	return &c
}

// deleteAll will delete all on disk data for ALL caches.
// Deletes are performed concurrently.
func (b *bucketMetacache) deleteAll() {
	b.mu.Lock()
	defer b.mu.Unlock()

	ctx := context.Background()
	ez, ok := newObjectLayerFn().(*erasureServerSets)
	if !ok {
		logger.LogIf(ctx, errors.New("bucketMetacache: expected objAPI to be *erasureZones"))
		return
	}

	b.updated = true
	if !b.transient {
		// Delete all.
		ez.deleteAll(ctx, minioMetaBucket, metacachePrefixForID(b.bucket, slashSeparator))
		b.caches = make(map[string]metacache, 10)
		return
	}

	// Transient are in different buckets.
	var wg sync.WaitGroup
	for id := range b.caches {
		wg.Add(1)
		go func(cache metacache) {
			defer wg.Done()
			ez.deleteAll(ctx, minioMetaBucket, metacachePrefixForID(cache.bucket, cache.id))
		}(b.caches[id])
	}
	wg.Wait()
	b.caches = make(map[string]metacache, 10)
}

// deleteCache will delete a specific cache and all files related to it across the cluster.
func (b *bucketMetacache) deleteCache(id string) {
	b.mu.Lock()
	c, ok := b.caches[id]
	if ok {
		delete(b.caches, id)
		b.updated = true
	}
	b.mu.Unlock()
	if ok {
		c.delete(context.Background())
	}
}